Electrophotographic photoreceptor and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that can control the state of dispersion of silica particles in a photosensitive layer and the state of the surface of the photosensitive layer to prevent the generation of stress cracks and obtain stable image characteristics for a long period, and an image forming apparatus.SOLUTION: An electrophotographic photoreceptor comprises a conductive support, and a photosensitive layer formed on the conductive support. The photosensitive layer is formed of one or more layers. A surface layer of the photosensitive layer contains a binder resin, silica particles, and a charge transport substance. The ten-point average roughness Rz of the surface of the surface layer is 0.08 μm or more and 0.80 μm or less, and the average interval Sm of the irregularities on the surface of the surface layer is more than 15 μm and 120 μm or less. The ratio of the average interval Sm to the ten-point average roughness Rz (Sm / Rz) is 30 or more and 500 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic photoreceptor and an image forming apparatus. [Background technology]

[0002] In recent years, organic photoconductors using organic photoconductive materials have been widely used as electrophotographic photoconductors (hereinafter simply referred to as "photoconductors"). However, due to the nature of organic materials, organic photoconductors have the drawback that their surfaces are easily worn away by contact with cleaning blades and the like.

[0003] In addition, with the recent increase in contact charging methods using roller charging and the trend toward longer life, smaller size, and higher speed of image forming devices such as digital copiers and printers, organic photoreceptors are exposed to harsh conditions in which their surfaces are more susceptible to wear.

[0004] To address this issue of wear on the surface of the photoreceptor, it has been considered to add inorganic compound particles such as silica particles or alumina particles as a filler to the surface layer of the photoreceptor.

[0005] For example, Patent Document 1 discloses a laminated electrophotographic photoreceptor that includes a photosensitive layer having a charge generation layer containing a charge generation agent (also referred to as a "charge generation substance") and a charge transport layer containing a charge transport agent (also referred to as a "charge transport substance"), a binder resin, a phthalocyanine pigment, and silica particles, wherein the charge transport layer is a single layer and is disposed as the outermost layer, the content of the silica particles is 0.5 parts by mass or more and 15 parts by mass or less per 100 parts by mass of the binder resin, and the average primary particle diameter of the silica particles is 50 nm or more and 150 nm or less.

[0006] Patent Document 2 discloses an electrophotographic photosensitive member used in an image forming apparatus having a charging means for an electrophotographic photosensitive member, an exposure means, a developing means for developing with a liquid developer containing toner, a primary transfer means for primarily transferring the toner image formed on the electrophotographic photosensitive member by the developing means onto an intermediate transfer member, and a secondary transfer means for transferring the toner image on the intermediate transfer member to a recording medium, the electrophotographic photosensitive member containing at least inorganic compound fine particles and organic compound fine particles in its surface layer, and discloses that the inorganic compound fine particles are preferably at least any one of silica particles, alumina particles, titanium dioxide particles, and strontium titanate particles having a particle diameter of 1 to 200 nm, and that the surface roughness (Rz) of the electrophotographic photosensitive member is preferably 0.2 to 1.5 μm.

[0007] Patent Document 3 discloses an electrophotographic photoreceptor having at least a photosensitive layer on a conductive support, the surface layer of which contains a modified polycarbonate copolymer resin containing a specific repeating unit and a repeating unit of a siloxane structure, and also contains silica particles having a volume average particle diameter of 0.005 μm or more and less than 0.05 μm.

[0008] Furthermore, it has been considered to form a curable protective layer (also called a "surface protective layer") on the charge transport layer and add inorganic compound particles such as silica particles as a filler to the curable protective layer, which is the surface layer.

[0009] For example, Patent Document 4 discloses an electrophotographic photoreceptor in which a photosensitive layer and a curable protective layer are sequentially provided on a conductive support, the curable protective layer containing a cured product of a radically polymerizable compound having three or more functionalities and a filler having a portion exposed from the surface of the curable protective layer, the surface of the curable protective layer having raised portions that rise along the surface of the filler, and where r is the radius of the filler contained in the curable protective layer and T is the film thickness of the curable protective layer, T>2r and formula (a) holds: 100×(number of fillers at a depth of T / 2 from the free surface of the curable protective layer / total number of fillers in the curable protective layer)≧70%.

[0010] Although dispersing fillers within the photosensitive layer can improve printing durability and achieve a long life, problems caused by contact with surrounding components, such as poor cleaning, are a major obstacle to practical application. These problems tend to be more pronounced when small-particle-size fillers are used; repeated electrical fatigue and the accumulation of mechanical fatigue during the cleaning process lead to the formation of aggregated structures of the small-particle-size fillers, which then cause stress cracks. Patent Document 5 attempts to optimize friction between the photosensitive layer surface and surrounding components (contact members) by forming linear scratches on the photosensitive layer surface, while Patent Document 6 attempts to optimize friction by controlling the surface properties of a high-print-durability photosensitive member using amorphous silicon. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-49519 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-86131 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-66800 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-108487 [Patent Document 5] Japanese Patent Application Laid-Open No. 2010-134459 [Patent Document 6] International Publication No. 2016 / 121231 Summary of the Invention [Problem to be solved by the invention]

[0012] However, in the above-mentioned prior art, when inorganic compound fine particles are contained in the surface layer of the photosensitive layer, it is difficult to achieve both improved abrasion resistance and stable image formation over a long period of time.

[0013] When inorganic compound particles are contained in the surface layer of the photosensitive layer, aggregates of the inorganic compound particles exist inside the photosensitive layer due to insufficient dispersibility of the inorganic compound particles. If the slipperiness of the photosensitive body surface is impaired by electrical fatigue due to roller charging or by the sliding of the cleaning blade (a process in which the cleaning blade removes toner remaining on the outer peripheral surface of the photosensitive body), the frictional resistance between the photosensitive body surface and the cleaning blade increases.

[0014] When inorganic compound particles are incorporated into a photosensitive layer, the binder resin has a larger thermal expansion coefficient than the inorganic compound particles, which causes shear stress at the interface between the inorganic compound particles and the binder resin. This stress concentrates around aggregates of the inorganic compound particles, leading to the problem of stress cracks. This phenomenon becomes more severe when the inorganic compound particles are insufficiently dispersible and when the frictional resistance between the photoreceptor surface and the cleaning blade increases with long-term use. Therefore, improving the dispersibility of the inorganic compound particles in the photosensitive layer, the smoothness of the photosensitive layer surface, and the mechanical strength of the photosensitive layer have been issues.

[0015] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide an electrophotographic photoreceptor and an image forming apparatus that can suppress the occurrence of stress cracks by controlling the dispersion state of silica particles in the photosensitive layer and the surface state of the photosensitive layer, thereby achieving stable image characteristics over a long period of time. [Means for solving the problem]

[0016] As a result of intensive research into solving the above problems, the present inventors have discovered that the stress crack resistance (hereinafter also simply referred to as "crack resistance") of a photosensitive body can be improved by optimizing the dispersion state of silica particles in a coating solution for forming a surface layer of a photosensitive body in order to improve the mechanical strength of the photosensitive layer, improve the dispersion uniformity of silica particles in the photosensitive layer, and control the shape of the surface of the photosensitive layer, and have thus completed the present invention.

[0017] That is, the electrophotographic photoreceptor according to the present invention comprises a conductive support and a photosensitive layer formed on the conductive support, the photosensitive layer being composed of one or more layers, the surface layer of the photosensitive layer containing a binder resin, silica particles, and a charge transport material, the ten-point mean roughness Rz of the surface of the surface layer being 0.08 μm or more and 0.80 μm or less, the mean spacing Sm of the irregularities on the surface of the surface layer being more than 15 μm and 120 μm or less, and the ratio Sm / Rz of the mean spacing Sm to the ten-point mean roughness Rz being 30 or more and 500 or less.

[0018] According to the electrophotographic photoreceptor, stress cracks do not occur in the photoreceptor even after long-term use, and therefore the photoreceptor can have a long life.

[0019] In the electrophotographic photoreceptor, the content of the silica particles in the surface layer is preferably 8% by mass or more and 25% by mass or less based on the total solid content of the surface layer, whereby the effect of abrasion resistance due to the addition of silica particles to the surface layer can be sufficiently obtained, and an electrophotographic photoreceptor with excellent cleanability can be realized.

[0020] In the electrophotographic photoreceptor, the elastic power of the photosensitive layer is preferably 41% or more and 48% or less, as measured by applying a maximum indentation load of 30 mN to the surface of the surface layer for 5 seconds in an environment of a temperature of 25° C. and a relative humidity of 50%, which can alleviate shear stress generated in the photosensitive layer.

[0021] In the electrophotographic photoreceptor, it is preferable that the photosensitive layer is composed of a charge generating layer and a charge transport layer, and that the thickness of the photosensitive layer is 25 μm or more, thereby realizing an electrophotographic photoreceptor that can provide stable image characteristics for a longer period of time.

[0022] In the electrophotographic photoreceptor, the number average primary particle diameter of the silica particles is preferably 10 nm or more and 30 nm or less, which makes it easier to control the average spacing Sm of the irregularities on the surface of the surface layer to be small.

[0023] In the electrophotographic photoreceptor, the ten-point height of roughness Rz is preferably 0.1 μm or more and 0.5 μm or less, in which case the dispersibility of silica particles in the surface layer of the photosensitive layer can be further improved.

[0024] In the electrophotographic photosensitive member, the average spacing Sm is preferably 20 μm or more and 50 μm or less, in which case the external stress on the surface layer caused by the cleaning blade can be further reduced.

[0025] In the electrophotographic photosensitive member, it is preferable that the ratio Sm / Rz of the average spacing Sm to the ten-point height of roughness Rz is 100 or more and 200 or less. In this case, an electrophotographic photosensitive member having excellent crack resistance and cleaning properties can be realized.

[0026] In the electrophotographic photoreceptor, the Vickers hardness (HV) of the photosensitive layer, measured by applying a maximum indentation load of 30 mN to the surface of the surface layer for 5 seconds in an environment of a temperature of 25° C. and a relative humidity of 50%, is preferably 26 or more. In this case, an electrophotographic photoreceptor that can provide stable image characteristics for a longer period of time can be realized.

[0027] In the electrophotographic photoreceptor, by providing an undercoat layer between the conductive support and the photosensitive layer (laminated photosensitive layer), electrophotographic properties such as charging properties can be maintained well throughout the life of the electrophotographic photoreceptor.

[0028] The image forming apparatus according to the present invention comprises the electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, exposure means for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, developing means for developing the electrostatic latent image formed by exposure to form a toner image, transfer means for transferring the toner image formed by development onto a recording medium, fixing means for fixing the transferred toner image on the recording medium to form an image, cleaning means for removing and recovering toner remaining on the electrophotographic photosensitive member, and discharging means for discharging surface charge remaining on the electrophotographic photosensitive member.

[0029] The image forming apparatus described above is equipped with the electrophotographic photoreceptor of the present invention, and therefore can obtain stable image characteristics over a long period of time. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide an electrophotographic photoreceptor and an image forming apparatus that can suppress the occurrence of stress cracks and provide stable image characteristics over a long period of time. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 2 is a diagram schematically showing the relationship between the load applied to the contact point between the electrophotographic photosensitive member and the cleaning blade and the average spacing Sm of irregularities on the surface of the surface layer. [Figure 2] 1 is a cross-sectional view schematically illustrating a configuration of an electrophotographic photoreceptor according to an embodiment of the present invention. [Figure 3] 1 is a side view schematically illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention includes an electrophotographic photoreceptor and an image forming apparatus, which will be described in detail below.

[0033] (1) Electrophotographic photoreceptor The electrophotographic photoreceptor of the present invention comprises a conductive support and a photosensitive layer formed on the conductive support, the photosensitive layer being composed of one or more layers, the surface layer of the photosensitive layer containing a binder resin, silica, and a charge transport material, the ten-point mean roughness Rz of the surface of the surface layer being 0.08 μm or more and 0.80 μm or less, the mean spacing Sm of the irregularities on the surface of the surface layer being more than 15 μm and 120 μm or less, and the ratio Sm / Rz of the mean spacing Sm to the ten-point mean roughness Rz being 30 or more and 500 or less.

[0034] 2 is a cross-sectional view schematically illustrating the configuration of an electrophotographic photoreceptor according to one embodiment of the present invention. The electrophotographic photoreceptor 1 is a laminated photoreceptor (also referred to as a "function-separated photoreceptor") in which a photosensitive layer 14 (also referred to as a "laminated photosensitive layer" or "function-separated photosensitive layer") having a laminated structure in which an undercoat layer 18 is laminated on a conductive support 11, and a charge generation layer 15 and a charge transport layer 16 are laminated on the undercoat layer 18 in this order is provided. The electrophotographic photoreceptor of the present invention may be a laminated photoreceptor in which a surface protective layer is further provided on the charge transport layer 16.

[0035] The surface layer of the photosensitive layer in the present invention means the layer located on the outermost surface side of the photosensitive layer. That is, when the electrophotographic photosensitive member of the present invention does not have a surface protective layer as shown in Fig. 2, the charge transport layer corresponds to the surface layer, and when the electrophotographic photosensitive member of the present invention has a surface protective layer, the surface protective layer corresponds to the surface layer.

[0036] <Electrophotographic photoreceptor, surface layer of photosensitive layer> In the electrophotographic photoreceptor of the present invention, silica particles are uniformly dispersed in the surface layer. The content of silica particles in the surface layer is preferably 8% by mass or more and 25% by mass or less, and more preferably 8% by mass or more and 15% by mass or less, based on the total solid content of the surface layer. If the content of silica particles is less than the above lower limit, the effect of improving abrasion resistance achieved by adding silica particles to the surface layer may not be sufficiently obtained. If the content of silica particles exceeds the above upper limit, the dispersibility of the silica particles may be insufficient, resulting in an increase in aggregates and a deterioration in cleanability.

[0037] In the electrophotographic photoreceptor of the present invention, the ten-point average roughness Rz of the surface layer is 0.08 μm or more and 0.80 μm or less, preferably 0.1 μm or more and 0.5 μm or less. This is achieved by appropriately and uniformly agglomerating inorganic compound fine particles (silica particles) having a small particle size. Generally, the larger the particle size of the inorganic compound fine particles, the higher the abrasion resistance, but this can cause chipping of the edge of the cleaning blade. In the present invention, by appropriately agglomerating inorganic compound fine particles having a small particle size, large particles are created, thereby improving abrasion resistance. Furthermore, since the inorganic compound fine particles having a small particle size are peeled off by the sliding of the cleaning blade, partial damage to the cleaning blade can be suppressed.

[0038] If Rz is less than the lower limit, the interaction between the inorganic compound particles is insufficient, making it difficult to obtain abrasion resistance. If Rz exceeds the upper limit, the inorganic compound particles aggregate too much, which is likely to cause part of the cleaning blade to chip when the elasticity of the edge portion of the cleaning blade decreases in a low-temperature, low-humidity environment. In this state, the remaining toner cannot be sufficiently removed, which can cause streak defects in the formed image.

[0039] The ten-point mean roughness Rz is an index of the state of aggregation of inorganic compound fine particles in the surface layer of the photosensitive member. In this specification, the ten-point mean roughness Rz is defined in JIS-B-0601 (1994), and means the difference in μm between the average elevation of the fifth highest peak and the average elevation of the fifth deepest valley, measured in a reference length extracted from the cross-sectional curve of the surface layer of the photosensitive member, from a line parallel to the mean line and not intersecting the cross-sectional curve in a direction perpendicular to the mean line.

[0040] In the present invention, the ten-point average roughness Rz of the surface of the surface layer and the average spacing Sm of the irregularities on the surface of the surface layer are measured by the method described in the Examples section below.

[0041] In the electrophotographic photoreceptor of the present invention, the average spacing Sm of irregularities on the surface of the surface layer is more than 15 μm and not more than 120 μm, preferably 20 μm or more and 50 μm or less, and more preferably 25 μm or more and 50 μm or less. When Sm is within the above range, external stress on the surface layer from the cleaning blade can be reduced, and the occurrence of stress cracks can be suppressed. Figure 1 shows an outline of the relationship between the load applied to the contact point between the electrophotographic photoreceptor and the cleaning blade and the average spacing Sm of irregularities on the surface of the surface layer. Stress cracks tend to worsen when Sm is greater or smaller than the above range. It is presumed that when Sm is within the above range, appropriate spacing between irregularities on the surface of the surface layer can be maintained, reducing friction between the surface of the surface layer and the cleaning blade.

[0042] In the electrophotographic photoreceptor of the present invention, Sm / Rz, which is the ratio of Sm to Rz, is 30 or more and 500 or less, and preferably 100 or more and 200 or less. By controlling Sm / Rz within the above range, external stress on the surface layer by the cleaning blade can be reduced, and the occurrence of stress cracks can be suppressed.

[0043] To control the surface condition of an electrophotographic photoreceptor so as to satisfy the above-mentioned Rz, Sm, and Sm / Rz requirements, it is necessary to optimize the dispersibility of silica particles in the surface layer of the photosensitive layer, and thus the dispersibility of silica particles in the surface layer-forming coating solution (hereinafter simply referred to as the "coating solution"). As a result of extensive research, the inventors have found that, as an example, the uniformity of dispersion of silica particles in the surface layer can be improved by contacting silica particles in the coating solution with a soda-lime glass material during the process of preparing the surface layer-forming coating solution. Soda-lime glass materials contain metal oxides with high contact electrification properties, including sodium oxide, potassium oxide, calcium oxide, magnesium oxide, and aluminum oxide. Therefore, during the coating solution preparation process, contacting the silica particles in the coating solution with the soda-lime glass charges the silica particles, generating charge repulsion between the silica particles, thereby improving dispersibility. The inventors have found that by controlling this coating solution preparation scheme, it is possible to control the dispersibility of silica particles in the coating solution and thereby control the surface properties of the photoreceptor. The electrophotographic photoreceptor of the present invention is not limited to those manufactured by the above-mentioned method, and may be manufactured by a method other than the above-mentioned method as long as it can realize a surface condition that satisfies the above-mentioned conditions of Rz, Sm, and Sm / Rz.

[0044] In the electrophotographic photoreceptor of the present invention, the elastic power of the photosensitive layer, measured by applying a maximum indentation load of 30 mN to the surface of the surface layer for 5 seconds in an environment of 25° C. and 50% relative humidity, is preferably 41% to 48%, more preferably 44% to 47%. It is presumed that by controlling the dispersion state of the silica particles in the photosensitive layer as described above and keeping the elastic power of the entire photosensitive layer within the above range, the shear stress generated in the photosensitive layer can be alleviated.

[0045] In the electrophotographic photoreceptor of the present invention, when the photosensitive layer is composed of a charge generating layer and a charge transport layer, the thickness of the photosensitive layer is preferably 25 μm or more and 45 μm or less, and more preferably 30 μm or more and 42 μm or less. When the thickness is within the above range, an electrophotographic photoreceptor can be realized which can obtain stable image characteristics for a longer period of time.

[0046] In the electrophotographic photoreceptor of the present invention, the number-average primary particle diameter of the silica particles contained in the surface layer of the photosensitive layer is preferably 10 nm or more and 30 nm or less, and more preferably 10 nm or more and 20 nm or less. When the number-average primary particle diameter of the silica particles is within the above range, it becomes easier to control the average spacing Sm of the irregularities on the surface of the surface layer to a small value. If the number-average primary particle diameter is below the above lower limit, the anchoring effect of the silica particles on the photosensitive layer may be insufficient, and sufficient abrasion resistance may not be maintained. If the number-average primary particle diameter exceeds the above upper limit, the aggregate structure of the silica particles generated in the photosensitive layer may become large, which may lead to problems such as poor cleaning.

[0047] The number average primary particle diameter of silica particles is measured by observing silica particles under a scanning electron microscope at a magnification of 30,000 to 300,000 times, for example, 100,000 times, observing 100 particles at random as primary particles, and determining the Feret's direction average diameter by image analysis.

[0048] In the electrophotographic photoreceptor of the present invention, the Vickers hardness (HV) of the photosensitive layer, measured by applying a maximum indentation load of 30 mN to the surface of the surface layer for 5 seconds in an environment of a temperature of 25°C and a relative humidity of 50%, is preferably 26 or more, more preferably 26.5 or more, and particularly preferably 26.5 to 28. When the Vickers hardness is within the above range, an electrophotographic photoreceptor can be realized which can provide stable image characteristics for a longer period of time.

[0049] <Conductive support> The conductive support has a function as an electrode of the photoreceptor and a function as a support member, and the material constituting the conductive support is not particularly limited as long as it is a material used in the relevant technical field.

[0050] Specific examples include metal materials such as aluminum, aluminum alloys, copper, zinc, stainless steel, and titanium; materials obtained by laminating metal foil onto the surface of polymer materials (polyethylene terephthalate, nylon, polystyrene, and the like), glass, hard paper, and the like; materials obtained by vapor-depositing a metal material onto these surfaces; and materials obtained by vapor-depositing or applying a layer of a conductive compound such as a conductive polymer, tin oxide, or indium oxide onto these surfaces. Among these, aluminum is preferred from the viewpoint of ease of processing, and aluminum alloys such as JIS3003, JIS5000, and JIS6000 series are more preferred.

[0051] The shape of the conductive support is not limited to a cylindrical (drum) shape as shown in FIG. 3, but may be a sheet shape, a columnar shape, an endless belt shape, or the like.

[0052] Furthermore, the surface of the conductive support may be subjected to anodizing film treatment, surface treatment with chemicals or hot water, coloring treatment, or diffuse reflection treatment such as surface roughening, as long as it does not affect the image quality, in order to prevent interference fringes caused by laser light.

[0053] <Undercoat layer> The electrophotographic photoreceptor of the present invention preferably has an undercoat layer (also called an "intermediate layer") between the conductive support and the photosensitive layer.

[0054] The undercoat layer generally covers and smooths the irregularities on the surface of the conductive support, improves the film-forming properties of the photosensitive layer (charge generating layer in Figure 2), suppresses peeling of the photosensitive layer from the conductive support, and improves adhesion between the conductive support and the photosensitive layer. Specifically, it prevents charge injection from the conductive support into the photosensitive layer, prevents a decrease in the chargeability of the photosensitive layer, and prevents image fogging (so-called black spots).

[0055] The undercoat layer can be formed, for example, by dissolving a binder resin in a suitable solvent to prepare a coating liquid for the undercoat layer, applying this coating liquid to the surface of the conductive support, and then drying to remove the organic solvent.

[0056] Examples of binder resins include binder resins similar to those contained in the photosensitive layer described below, as well as natural polymer materials such as casein, gelatin, polyvinyl alcohol, and ethyl cellulose. One of these may be used alone, or two or more may be used in combination.

[0057] The binder resin is required to have properties such as not dissolving or swelling in the solvent used when forming the photosensitive layer on the undercoat layer, having excellent adhesion to the conductive support, and having flexibility. Therefore, among the above binder resins, polyamide resins are preferred, and alcohol-soluble nylon resins are particularly preferred.

[0058] Examples of alcohol-soluble nylon resins include homopolymer or copolymer nylons such as 6-nylon, 66-nylon, 610-nylon, 11-nylon, and 12-nylon, and resins obtained by chemically modifying nylons such as N-alkoxymethyl-modified nylons.

[0059] Examples of solvents for dissolving or dispersing resin materials include water, alcohols such as methanol, ethanol, and butanol; glymes such as methyl carbitol and butyl carbitol; chlorine-based solvents such as dichloroethane, chloroform, and trichloroethane; acetone, dioxolane, and mixed solvents of two or more of these solvents. Among these solvents, non-halogen organic solvents are preferably used in consideration of the global environment.

[0060] . The coating solution for the undercoat layer may also contain inorganic compound fine particles. The inorganic compound fine particles of the undercoat layer have a different purpose from the inorganic compound fine particles contained in the surface layer of the photosensitive layer, and may be the same compound or different compounds.

[0061] The inorganic compound fine particles can easily adjust the volume resistivity of the undercoat layer, further suppress the injection of charges into the photosensitive layer, and maintain the electrical properties of the photoreceptor under various environments.

[0062] Examples of inorganic compound fine particles include titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide.

[0063] The ratio (C / D) of the total weight C of the binder resin and inorganic compound particles to the weight D of the solvent in the coating liquid for the undercoat layer is preferably 1 / 99 to 40 / 60, particularly preferably 2 / 98 to 30 / 70.

[0064] The ratio E / F of the weight E of the binder resin to the weight F of the inorganic compound fine particles is preferably 90 / 10 to 1 / 99, and particularly preferably 70 / 30 to 5 / 95.

[0065] In order to disperse the inorganic compound particles in the coating liquid for the undercoat layer, known devices such as a ball mill, a sand mill, an attritor, a vibration mill, an ultrasonic disperser, and a paint shaker may be used.

[0066] The coating method for the undercoat layer coating liquid may be appropriately selected from among the most suitable methods taking into consideration the physical properties of the coating liquid, productivity, and the like. Examples of the coating method include spraying, bar coating, roll coating, blade coating, ring coating, and dip coating.

[0067] Among these, the dip coating method is a method in which a substrate is immersed in a coating tank filled with a coating liquid and then pulled up at a constant speed or a gradually changing speed to form a layer on the surface of the substrate, and is relatively simple and excellent in terms of productivity and cost, so it can be suitably used for producing electrophotographic photoreceptors. The apparatus used for the dip coating method may be provided with a coating liquid dispersion device, typified by an ultrasonic generator, in order to stabilize the dispersibility of the coating liquid.

[0068] In the drying step of the formed undercoat layer, the solvent in the coating film may be removed by natural drying or may be removed by heating.

[0069] The temperature in the drying step is not particularly limited as long as it is a temperature at which the solvent used can be removed, but a temperature of about 50°C to 140°C is appropriate, and a temperature of about 80°C to 130°C is particularly preferred.

[0070] If the drying temperature is below 50°C, the drying time may be long and the solvent may not evaporate sufficiently and remain in the photosensitive layer.If the drying temperature exceeds 140°C, the electrical characteristics may deteriorate when the photoreceptor is used repeatedly, and the obtained image may be degraded.

[0071] Such temperature conditions are common not only to the undercoat layer but also to the formation of layers such as the photosensitive layer, which will be described later, and other treatments.

[0072] The thickness of the undercoat layer is not particularly limited, but is preferably 0.01 μm to 20 μm, more preferably 0.05 μm to 10 μm. If the thickness of the undercoat layer is less than 0.01 μm, the undercoat layer will not substantially function as an undercoat layer, and it may not be possible to cover defects in the conductive support to obtain a uniform surface, and it may not be possible to prevent charge injection from the conductive support to the photosensitive layer. On the other hand, if the thickness of the undercoat layer exceeds 20 μm, it may be difficult to form a uniform undercoat layer, and the sensitivity of the photoreceptor may also be reduced.

[0073] When the conductive support is made of aluminum, a layer containing alumite (alumite layer) can be formed as an undercoat layer.

[0074] The charge generation layer has the function of generating charges by absorbing light irradiated by a semiconductor laser beam or the like in an image forming apparatus or the like, and contains a charge generation substance as a main component and, if necessary, a binder resin and additives.

[0075] Charge-generating materials can be compounds commonly used in the art, including azo pigments such as monoazo pigments, bisazo pigments, and trisazo pigments; indigo pigments such as indigo and thioindigo; perylene pigments such as perylene imide and perylene anhydride; polycyclic quinone pigments such as anthraquinone and pyrenequinone; phthalocyanine pigments such as metal phthalocyanines and metal-free phthalocyanines, including titanyl phthalocyanine; organic photoconductive materials such as squarylium dyes, pyrylium salts, thiopyrylium salts, and triphenylmethane dyes; and inorganic photoconductive materials such as selenium and amorphous silicon. These charge-generating materials can be used alone or in combination.

[0076] Among these charge generating materials, those represented by the following general formula (A): [ka] (In the formula, X 1 , X 2 , X 3 and X 4 are each independently a halogen atom, an alkyl group, or an alkoxy group. 1 , X 2 , X 3 and X 4 may be the same or different. r, s, y, and z are each independently an integer of 0 to 4. r, s, y, and z may be the same or different. It is preferable to use titanyl phthalocyanine represented by the following formula:

[0077] Titanyl phthalocyanine is a charge-generating material that has high charge generation and injection efficiencies in the emission wavelength range (near-infrared light) of currently commonly used laser light and LED light. It generates a large amount of charge by absorbing light and can efficiently inject the generated charge into a charge-transporting material without accumulating it internally.

[0078] The titanyl phthalocyanine represented by the general formula (A) can be produced by known production methods, such as the method described in Phthalocyanine Compounds by Moser, Frank H. and Arthur L. Thomas, Reinhold Publishing Corp., New York, 1963.

[0079] For example, among the titanyl phthalocyanine compounds represented by general formula (A), unsubstituted titanyl phthalocyanine in which r, s, y, and z are 0 can be obtained by synthesizing dichlorotitanyl phthalocyanine by heating and melting phthalonitrile and titanium tetrachloride or by heating and reacting them in a suitable solvent such as α-chloronaphthalene, and then hydrolyzing the resultant with a base or water.

[0080] Alternatively, a titanyl phthalocyanine composition can be produced by reacting isoindoline with a titanium tetraalkoxide such as tetrabutoxytitanium under heating in a suitable solvent such as N-methylpyrrolidone.

[0081] Methods for forming a charge generation layer include vacuum deposition of a charge generation material onto a conductive support, and coating of a coating liquid for a charge generation layer obtained by dispersing a charge generation material in a solvent onto a conductive support. Among these, a preferred method is to disperse a charge generation material in a binder resin solution obtained by mixing a binder resin in a solvent using a conventionally known method, and then coat the coating liquid for a charge generation layer onto the conductive support (on the undercoat layer). This method will be described below.

[0082] The binder resin is not particularly limited, and any resin known in the art can be used, such as polyester, polystyrene, polyurethane, phenolic resin, alkyd resin, melamine resin, epoxy resin, silicone resin, acrylic resin, methacrylic resin, polycarbonate, polyarylate, polyphenoxy, polyvinyl butyral, polyvinyl formal, and the like, as well as copolymer resins containing two or more of the repeating units constituting these resins.

[0083] Examples of copolymer resins include insulating resins such as vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, acrylonitrile-styrene copolymer resin, etc. These resins may be used alone or in combination of two or more.

[0084] Examples of the solvent include halogenated hydrocarbons such as dichloromethane and dichloroethane; ketones such as acetone, methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as tetrahydrofuran (THF) and dioxane; alkyl ethers of ethylene glycol such as 1,2-dimethoxyethane; aromatic hydrocarbons such as benzene, toluene and xylene; and aprotic polar solvents such as N,N-dimethylformamide and N,N-dimethylacetamide. These solvents may be used alone or in combination of two or more.

[0085] The compounding ratio of the charge generating substance to the binder resin is preferably such that the proportion of the charge generating substance is in the range of 10 to 99% by mass.

[0086] If the proportion of the charge generating substance is less than 10% by mass, the sensitivity may decrease. On the other hand, if the proportion of the charge generating substance exceeds 99% by mass, not only will the film strength of the charge generating layer decrease, but the dispersibility of the charge generating substance will decrease, resulting in an increase in coarse particles, which will reduce the surface charge in areas other than those that should be erased by exposure, and may result in image defects, particularly image fog known as black spots, in which toner adheres to a white background and forms tiny black dots.

[0087] Before dispersing the charge generation material in the binder resin solution, the charge generation material may be pulverized in advance using a pulverizer such as a ball mill, sand mill, attritor, vibration mill, or ultrasonic disperser.

[0088] Examples of dispersing machines used to disperse the charge generating material in the binder resin solution include a paint shaker, a ball mill, a sand mill, etc. Dispersion conditions at this time should be selected appropriately so as to prevent the incorporation of impurities due to wear of the container and components of the dispersing machine used.

[0089] The coating liquid for the charge generating layer may be applied by the same method as the coating liquid for the undercoat layer, and a dip coating method is particularly preferred.

[0090] The thickness of the charge generating layer is not particularly limited, but is preferably 0.05 μm to 5 μm, more preferably 0.1 μm to 1 μm. If the thickness of the charge generating layer is less than 0.05 μm, the efficiency of light absorption may decrease, and the sensitivity of the photoreceptor may decrease. On the other hand, if the thickness of the charge generating layer exceeds 5 μm, charge transfer within the charge generating layer may become the rate-limiting step in the process of erasing the charge on the surface of the photoreceptor, and the sensitivity of the photoreceptor may decrease.

[0091] <Charge transport layer> The charge transport layer has the function of receiving the charges generated by the charge generating material and transporting them to the surface of the photoreceptor, and contains a charge transport material, a binder resin, and, if necessary, additives. When the charge transport layer corresponds to the surface layer of the photosensitive layer as shown in Figure 2, the charge transport layer in the present invention has the surface layer configuration described in the section <Surface layer of electrophotographic photoreceptor and photosensitive layer>.

[0092] The charge transport material may be a compound used in the art. Specific examples include carbazole derivatives, pyrene derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, polycyclic aromatic compounds, indole derivatives, pyrazoline derivatives, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, triarylmethane derivatives, phenylenediamine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives, benzidine derivatives, polymers having groups derived from these compounds in the main chain or side chain (such as poly-N-vinylcarbazole, poly-1-vinylpyrene, ethylcarbazole-formaldehyde resin, triphenylmethane polymer, poly-9-vinylanthracene, etc.), and polysilanes. These charge transport materials may be used alone or in combination of two or more.

[0093] A preferred method for forming the charge transport layer is to disperse the charge transport material and inorganic compound particles in a binder resin solution obtained by mixing a binder resin in a solvent by a known method, and then apply the coating liquid for the charge transport layer onto the charge generating layer. This method is described below.

[0094] The binder resin is not particularly limited, and any resin known in the art can be used, for example, vinyl polymer resins such as polymethyl methacrylate, polystyrene, polyvinyl chloride, and copolymer resins thereof; resins such as polycarbonate, polyester, polyester carbonate, polysulfone, polyphenoxy, epoxy resin, silicone resin, polyarylate, polyphenylene oxide, polyamide, polyether, polyurethane, polyacrylamide, and phenolic resin; and thermosetting resins obtained by partially crosslinking these resins. These binder resins may be used alone or in combination of two or more.

[0095] Among these, polystyrene, polycarbonate, and polyarylate have a volume resistivity of 10 13 It is particularly preferred that the resistance is Ω or more, which is excellent in electrical insulation, film-forming properties, potential characteristics, etc.

[0096] The ratio A / B of the charge transport material (A) to the binder resin (B) is preferably 10 / 12 to 10 / 30. If the ratio A / B is less than 10 / 30 and the binder resin ratio is high, the viscosity of the coating solution increases when the charge transport layer is formed by dip coating, resulting in a decrease in coating speed and significantly reduced productivity. Furthermore, if the amount of solvent in the coating solution is increased to suppress the increase in viscosity, blushing may occur, causing the formed charge transport layer to become cloudy. On the other hand, if the ratio A / B exceeds 10 / 12 and the binder resin ratio is low, the printing durability may be reduced compared to when the binder resin ratio is high, and the amount of wear of the photosensitive layer may increase.

[0097] The charge transport layer may contain inorganic compound particles or organic compound particles in order to increase the mechanical strength and improve the electrical properties.

[0098] When the charge transport layer corresponds to the surface layer of the photosensitive layer, the content of silica particles as inorganic compound fine particles is as described in the section <Surface layer of electrophotographic photosensitive member and photosensitive layer>. When the photosensitive layer has a surface protective layer, the content of inorganic compound fine particles in the charge transport layer is preferably 10% by mass or more and 25% by mass or less based on the total solid content of the charge transport layer.

[0099] The charge transport layer may contain additives such as a plasticizer and a leveling agent, if necessary, in order to improve film-forming properties, flexibility, and surface smoothness.

[0100] Examples of the plasticizer include dibasic acid esters such as phthalate esters, fatty acid esters, phosphate esters, chlorinated paraffin, epoxy-type plasticizers, etc. Examples of the leveling agent include silicon-based leveling agents, etc.

[0101] Examples of solvents include aromatic hydrocarbons such as benzene, toluene, xylene, and monochlorobenzene; halogenated hydrocarbons such as dichloromethane and dichloroethane; ethers such as THF, dioxane, and dimethoxymethyl ether; and aprotic polar solvents such as N,N-dimethylformamide. If necessary, solvents such as alcohols, acetonitrile, and methyl ethyl ketone can also be added. Among these solvents, non-halogenated organic solvents are preferred in consideration of the global environment. These solvents may be used alone or in combination of two or more.

[0102] The charge transport layer can be formed, for example, in the same manner as in the case of forming the charge generation layer described above, by preparing a coating liquid for the charge transport layer by dissolving or dispersing a charge transport material, a binder resin, and, if necessary, the additives described above in an appropriate solvent, and then applying this coating liquid onto the charge generation layer by a spray method, a bar coating method, a roll coating method, a blade method, a ring coating method, a dip coating method, etc. Among these coating methods, the dip coating method is particularly preferable for forming the charge transport layer because it has various advantages as described above.

[0103] The thickness of the charge transport layer is not particularly limited, but is preferably 5 μm to 50 μm, more preferably 10 μm to 40 μm. If the thickness of the charge transport layer is less than 5 μm, the charge retention ability of the photoreceptor surface may decrease. On the other hand, if the thickness of the charge transport layer is more than 50 μm, the resolution of the photoreceptor may decrease.

[0104] <Surface protective layer> As described above, the electrophotographic photoreceptor of the present invention may further have a surface protective layer provided on the charge transport layer. When such a surface protective layer is provided, the surface protective layer corresponds to the surface layer, and the surface protective layer in the present invention has the surface layer configuration described in the section <Surface layer of electrophotographic photoreceptor and photosensitive layer>.

[0105] The surface protective layer has a function of improving the durability of the photoreceptor, and contains a binder resin and inorganic compound fine particles, and optionally contains additives. The surface protective layer may also contain one or more of the same charge transport materials as those in the charge transport layer to stabilize electrical properties.

[0106] As the binder resin, a resin having binding properties used in the relevant field can be used, such as polystyrene, polyacetal, polyethylene, polycarbonate, polyarylate, polysulfone, polypropylene, polyvinyl chloride, etc. These binder resins may be used alone or in combination of two or more.

[0107] Among these, polycarbonate and polyarylate are particularly preferred in view of wear characteristics and electrical characteristics.

[0108] The surface protective layer can be formed, for example, in the same manner as in the case of forming the charge generating layer and the charge transport layer described above, by preparing a coating liquid for the surface protective layer by dissolving or dispersing a binder resin and inorganic compound fine particles, and, if necessary, the additives described above, in an appropriate solvent, and then applying this coating liquid onto the charge transport layer by a spray method, a bar coating method, a roll coating method, a blade method, a ring coating method, a dip coating method, etc. Among these coating methods, the dip coating method is particularly preferable when forming the surface protective layer because it is superior in various respects as described above.

[0109] The thickness of the surface protective layer is not particularly limited, but is preferably 0.1 μm or more and 10 μm or less, and more preferably 1.0 μm or more and 8.0 μm or less.

[0110] Photoconductors intended for long-term, repeated use are designed to be mechanically durable and resistant to wear. However, in actual equipment, ozone and NOx gases are generated from charging components and adhere to the surface of the photoconductor, causing image deletion. To prevent this image deletion, the photosensitive layer must be worn at a certain rate or faster. Considering long-term, repeated use, a surface protective layer with a thickness of at least 1.0 μm is preferable. Furthermore, if the thickness of the surface protective layer exceeds 8.0 μm, problems such as an increase in residual potential and a decrease in fine dot reproducibility may occur.

[0111] (2) Image forming device The image forming apparatus of the present invention is characterized by comprising at least the photoreceptor of the present invention, a charging means for charging the photoreceptor, an exposure means for exposing the charged photoreceptor to light to form an electrostatic latent image, a developing means for developing the electrostatic latent image formed by exposure to form a toner image (visible image), a transfer means for transferring the toner image formed by development onto a recording medium, a fixing means for fixing the transferred toner image on the recording medium to form an image, a cleaning means for removing and recovering toner remaining on the photoreceptor, and a discharging means for discharging surface charges remaining on the photoreceptor. The image forming apparatus of the present invention will be described below with reference to the drawings, but the image forming apparatus of the present invention is not limited thereto.

[0112] Fig. 3 is a side view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus (laser printer) 100 in Fig. 3 includes the photoreceptor 1 of the present invention, an exposure means (semiconductor laser) 31, a charging means (charger) 32, a developing means (developer) 33, a transfer means (transfer charger) 34, a conveyor belt (not shown), a fixing means (fixer) 35, and a cleaning means (cleaner) 36. Reference numeral 51 denotes a recording medium (recording paper or transfer paper).

[0113] Photoreceptor 1 is rotatably supported on the main body of image forming apparatus 100 and is driven to rotate around rotation axis 44 in the direction of arrow 41 by driving means (not shown). The driving means includes, for example, an electric motor and a reduction gear, and transmits its driving force to a conductive support constituting the core of photoreceptor 1, thereby driving and rotating photoreceptor 1 at a predetermined peripheral speed. Charging means (charger) 32, exposure means (semiconductor laser) 31, developing means (developer) 33, transfer means (transfer charger) 34, and cleaning means (cleaner) 36 are provided in this order along the outer circumferential surface of photoreceptor 1 from upstream to downstream in the direction of rotation of photoreceptor 1, as indicated by arrow 41.

[0114] The charger 32 is a charging means for uniformly charging the outer circumferential surface of the photosensitive member 1 to a predetermined potential.

[0115] The exposure means 31 has a semiconductor laser as a light source, and irradiates the surface of the photoreceptor 1 between the charger 32 and the developer 33 with a laser beam light output from the light source, thereby exposing the charged outer peripheral surface of the photoreceptor 1 according to image information. The light is repeatedly scanned in the main scanning direction, that is, the direction of extension of the rotation axis 44 of the photoreceptor 1, and these are focused to sequentially form electrostatic latent images on the surface of the photoreceptor 1. In other words, the amount of charge on the photoreceptor 1, which has been uniformly charged by the charger 32, differs depending on whether or not it is irradiated with the laser beam, thereby forming an electrostatic latent image.

[0116] The developing device 33 is a developing means that develops the electrostatic latent image formed on the surface of the photosensitive member 1 by exposure with a developer (toner), and is provided facing the photosensitive member 1 and includes a developing roller 33a that supplies toner to the outer peripheral surface of the photosensitive member 1, and a casing 33b that supports the developing roller 33a rotatably around a rotation axis parallel to the rotation axis 44 of the photosensitive member 1 and contains a developer containing toner in its internal space.

[0117] The transfer charger 34 is a transfer means that transfers a toner image, which is a visible image formed on the outer peripheral surface of the photosensitive member 1 by development, onto transfer paper 51, which is a recording medium that is supplied between the photosensitive member 1 and the transfer charger 34 from the direction of arrow 42 by a transport means (not shown). The transfer charger 34 is, for example, a contact-type transfer means that includes a charging means and transfers the toner image onto the transfer paper 51 by applying a charge of the opposite polarity to that of the toner to the transfer paper 51.

[0118] The cleaner 36 is a cleaning means that removes and collects toner remaining on the outer peripheral surface of the photoreceptor 1 after the transfer operation by the transfer charger 34, and includes a cleaning blade 36a that separates the toner remaining on the outer peripheral surface of the photoreceptor 1, and a collection casing 36b that contains the toner separated by the cleaning blade 36a. The cleaner 36 is also provided together with a static elimination lamp (not shown).

[0119] The image forming apparatus 100 is also provided with a fixing device 35, which is a fixing means for fixing the transferred image, downstream of the transport of the transfer paper 51 that has passed between the photoreceptor 1 and the transfer charger 34. The fixing device 35 is provided with a heating roller 35a having a heating means (not shown), and a pressure roller 35b that is provided opposite the heating roller 35a and is pressed against the heating roller 35a to form a contact portion.

[0120] Reference numeral 37 denotes a separating means for separating the transfer paper from the photosensitive member, and reference numeral 38 denotes a casing that houses the above-mentioned means provided in the image forming apparatus.

[0121] The image forming operation by this image forming apparatus 100 is performed as follows.

[0122] First, when the photosensitive member 1 is rotated in the direction of arrow 41 by the driving means, the surface of the photosensitive member 1 is uniformly charged to a predetermined positive potential by the charger 32, which is located upstream of the image-forming point of the light by the exposure means 31 in the direction of rotation of the photosensitive member 1.

[0123] Next, light corresponding to image information is irradiated from exposure means 31 onto the surface of photoreceptor 1. This exposure removes surface charge from the areas of photoreceptor 1 that have been irradiated with light, creating a difference in surface potential between the areas that have been irradiated with light and the areas that have not been irradiated with light, forming an electrostatic latent image.

[0124] Toner is supplied from a developing device 33, which is located downstream in the rotational direction of the photosensitive member 1 from the imaging point of the light by the exposure means 31, to the surface of the photosensitive member 1 on which the electrostatic latent image is formed, thereby developing the electrostatic latent image and forming a toner image.

[0125] In synchronization with the exposure of the photoreceptor 1, transfer paper 51 is supplied between the photoreceptor 1 and transfer charger 34. The transfer charger 34 imparts a charge of opposite polarity to that of the toner to the supplied transfer paper 51, and the toner image formed on the surface of the photoreceptor 1 is transferred onto the transfer paper 51.

[0126] The transfer paper 51 onto which the toner image has been transferred is transported by the transport means to the fixing device 35, and is heated and pressed as it passes through the contact area between the heating roller 35a and the pressure roller 35b of the fixing device 35, and the toner image is fixed onto the transfer paper 51 to form a solid image. The transfer paper 51 on which the image has been formed in this way is discharged to the outside of the image forming apparatus 100 by the transport means.

[0127] Meanwhile, the toner remaining on the surface of the photoreceptor 1 after the transfer of the toner image by the transfer charger 34 is peeled off and collected from the surface of the photoreceptor 1 by the cleaner 36. The charge on the surface of the photoreceptor 1 from which the toner has been removed in this way is removed by light from the discharging lamp, and the electrostatic latent image on the surface of the photoreceptor 1 disappears. Thereafter, the photoreceptor 1 is further rotated, and the series of operations starting with charging are repeated again, forming images continuously. [Example]

[0128] The present invention will be described below based on examples and comparative examples, but the present invention is not limited to these examples.

[0129] [Example 1] (Formation of undercoat layer) Three parts by weight of titanium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., product name: Tybake TTO-D-1) and two parts by weight of copolymer polyamide (nylon) (manufactured by Toray Industries, Inc., product name: Amilan (registered trademark), grade: CM8000) were added to 25 parts by weight of methyl alcohol, and the mixture was dispersed for eight hours using a paint shaker to prepare three liters of a coating solution for the undercoat layer.

[0130] The obtained coating liquid for the undercoat layer was filled into a coating tank, and an aluminum drum-shaped support having a diameter of 30 mm and a length of 255 mm, which served as the conductive support 11, was immersed in it and then removed. The resulting coating film was allowed to dry naturally, forming an undercoat layer 18 with a thickness of 1 μm on the conductive support 11.

[0131] (Formation of Charge Generation Layer) Titanyl phthalocyanine represented by the following formula, which was to be used as a charge generating material, was prepared in advance. [ka]

[0132] 29.2 g of diiminoisoindoline and 200 ml of sulfolane were mixed, and 17.0 g of titanium tetraisopropoxide was added, followed by reaction under a nitrogen atmosphere at 140° C. for 2 hours. The resulting reaction mixture was allowed to cool, and the precipitate was collected by filtration, washed successively with chloroform and a 2% aqueous solution of hydrochloric acid, and then washed successively with water and methanol, and dried to obtain 25.5 g of blue-purple crystals.

[0133] Chemical analysis of the obtained crystals confirmed that they were titanyl phthalocyanine represented by the above structural formula (yield: 88.5%).

[0134] One part by mass of the obtained titanyl phthalocyanine and one part by mass of butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BM-2) were added to 98 parts by mass of methyl ethyl ketone, and the mixture was dispersed for two hours using a paint shaker to prepare 3 liters of coating liquid for the charge generating layer.

[0135] The obtained coating liquid for the charge generating layer was applied onto the undercoat layer 18 using the same immersion method as in the case of forming the undercoat layer, and the obtained coating film was allowed to dry naturally to form a charge generating layer 15 with a film thickness of 0.3 μm.

[0136] (Formation of charge transport layer) Next, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) were suspended in 14.2 g of tetrahydrofuran in a soda-lime glass container and stirred for 30 hours using a stirring blade. To the resulting silica filler suspension, 11.0 g of compound (1) represented by the following formula as a charge transport material, 21.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 122.6 g of tetrahydrofuran were added, mixed, and stirred for an additional 15 hours. The resulting mixture was degassed for 3 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A particle dispersing device (manufactured by Microfluidics, model: M-110P) was used to perform a 5-pass dispersion process to prepare a coating solution for the charge transport layer, which was then allowed to stand at 20°C for 1 day. [ka]

[0137] The obtained coating liquid for the charge transport layer was applied onto the charge generation layer 15 by the same immersion method as in the case of forming the undercoat layer, and the obtained coating film was dried at 115°C for 1.5 hours to form a surface layer (charge transport layer) 16 with a thickness of 35 μm, thereby obtaining the electrophotographic photoreceptor of Example 1 as schematically shown in Figure 2.

[0138] The compound (1) (stilbene compound) used was prepared in advance based on the method described in Japanese Patent No. 3272257.

[0139] [Example 2] An electrophotographic photosensitive member of Example 2 was produced in the same manner as in Example 1, except that the silica particles used in preparing the silica filler suspension of Example 1 were changed to AEROSIL R974 (trade name, manufactured by Nippon Aerosil Co., Ltd., number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment).

[0140] [Example 3] An electrophotographic photosensitive member of Example 3 was produced in the same manner as in Example 1, except that the silica particles used in preparing the silica filler suspension of Example 1 were changed to AEROSIL R976 (trade name, manufactured by Nippon Aerosil Co., Ltd., number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment).

[0141] [Example 4] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0142] Silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL RX50, number average primary particle diameter 40 nm, bulk density 0.17 g / cm) were placed in a soda-lime glass container. 3 , true density 2.65g / cm 3 4 g of a charge transport material (4 g of hexamethyldisilazane surface treatment), 11.0 g of compound (1) represented by the above formula as a charge transport material, 21.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 136.8 g of tetrahydrofuran were added and mixed, followed by stirring for an additional 30 hours. The resulting mixture was degassed for 3 minutes using a Foamer Blender ARE-310 (manufactured by Thinky Corporation). A five-pass dispersion process was performed using a particle dispersion device (manufactured by Microfluidics, model: M-110P) to prepare a charge transport layer coating solution, which was then allowed to stand at 20°C. An electrophotographic photoreceptor of Example 4 was produced in the same manner as in Example 1, except for the above procedures.

[0143] [Example 5] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0144] In a soda-lime glass container, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment) were suspended in 18.2 g of tetrahydrofuran and stirred for 40 hours using a stirring blade. To the resulting silica filler suspension, 11.0 g of compound (1) represented by the above formula as a charge transport material, 21.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 118.6 g of tetrahydrofuran were added, mixed, and further stirred for 15 hours. The resulting mixture was degassed for 5 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A coating solution for the charge transport layer was prepared by five-pass dispersion using a particle dispersing device (manufactured by Microfluidics, model: M-110P) and allowed to stand at 20°C for 1 week. An electrophotographic photoreceptor of Example 5 was fabricated in the same manner as in Example 1, except for the above procedures.

[0145] [Example 6] An electrophotographic photoreceptor of Example 6 was produced in the same manner as in Example 4, except that in preparing the coating solution for the charge transport layer, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL 9200, number average primary particle diameter 12 nm, structurally modified after dimethyldichlorosilane surface treatment), 11.0 g of compound (1) represented by the above formula as a charge transport material, 21.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., trade name: TS2050), and 136.8 g of tetrahydrofuran were added and mixed.

[0146] [Example 7] The electrophotographic photosensitive member of Example 7 was produced in the same manner as in Example 1, except that in preparing the coating solution for the charge transport layer, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) and 36 g of tetrahydrofuran were added to a polypropylene container, soda-lime glass beads with a diameter of 2 mm were added, and the mixture was stirred for an additional 15 hours in a ball mill. After that, the glass beads were removed, and then 9.1 g of compound (1) represented by the above formula as a charge transport material, 17.7 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., trade name: TS2040), and 79.8 g of tetrahydrofuran were added, mixed, and stirred for 30 hours.

[0147] [Example 8] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0148] Silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL RX50, number average primary particle diameter 40 nm, bulk density 0.17 g / cm) were placed in a soda-lime glass container. 3 , true density 2.65g / cm 3 4 g of silica filler (surface-treated with hexamethyldisilazane) was suspended in 18.2 g of tetrahydrofuran and stirred for 40 hours using a stirring blade. 8.3 g of compound (1) represented by the above formula as a charge transport material, 16.2 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 103.6 g of tetrahydrofuran were added to the obtained silica filler suspension, mixed, and further stirred for 15 hours. The obtained mixture was degassed for 5 minutes using a Foamer Refiner ARE-310 (manufactured by Thinky Corporation). A coating solution for the charge transport layer was prepared by five-pass dispersion treatment using a particle dispersion device (manufactured by Microfluidics, model: M-110P) and allowed to stand at 20°C. An electrophotographic photoreceptor of Example 8 was produced in the same manner as in Example 1, except for the above procedures.

[0149] [Example 9] An electrophotographic photoreceptor of Example 9 was produced in the same manner as in Example 4, except that in preparing the coating solution for the charge transport layer, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment), 11.0 g of compound (1) represented by the above formula as a charge transport material, 21.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., trade name: TS2050), and 136.8 g of tetrahydrofuran were added and mixed.

[0150] [Example 10] An electrophotographic photoreceptor of Example 10 was produced in the same manner as in Example 1, except that in preparing the coating solution for the charge transport layer, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) and 36 g of tetrahydrofuran were added to a polypropylene container, soda-lime glass beads with a diameter of 2 mm were added, and the mixture was stirred for an additional 15 hours in a ball mill. After that, the glass beads were removed, and then 11.0 g of compound (1) represented by the above formula as a charge transport material, 21.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., trade name: TS2050), and 100.8 g of tetrahydrofuran were added, mixed, and stirred for 30 hours.

[0151] [Example 11] A charge transport layer having a thickness of 20 μm was prepared in the same manner as in Example 2. Next, the charge transport layer coating liquid of Example 7 was used as a surface protective layer coating liquid and spray-coated onto the charge transport layer 16. The resulting coating film was dried at 120° C. for 0.5 hours to form a surface protective layer having a thickness of 15 μm, thereby preparing an electrophotographic photoreceptor of Example 11 having a surface protective layer as the surface layer.

[0152] [Example 12] A coating liquid for a charge transport layer was prepared in the same manner as in Example 1, except that the silica particles used in preparing the silica filler suspension of Example 1 were changed to AEROSIL R972 (trade name, manufactured by Nippon Aerosil Co., Ltd., number average primary particle diameter 16 nm, dimethyldichlorosilane surface treatment). An electrophotographic photoreceptor of Example 12 was produced in the same manner as in Example 1, except that a charge transport layer having a film thickness of 28 μm was formed in the charge transport layer formation step.

[0153] [Example 13] An electrophotographic photoreceptor of Example 13 was produced in the same manner as in Example 12, except that a charge transport layer having a thickness of 24 μm was formed in the charge transport layer forming step.

[0154] [Example 14] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0155] In preparing the silica filler suspension of Example 1, the silica particles were changed to AEROSIL R976 (trade name, manufactured by Nippon Aerosil Co., Ltd., number average primary particle diameter 16 nm, dimethyldichlorosilane surface treatment), and a silica filler suspension was obtained. To the obtained silica filler suspension, 11.0 g of compound (1) represented by the above formula as a charge transport material, 21.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., trade name: TS2040), and 122.6 g of tetrahydrofuran were added, mixed, and further stirred for 15 hours. The resulting mixture was degassed for 5 minutes using a Foamer Refiner ARE-310 (manufactured by Thinky Corporation). A five-pass dispersion process was performed using a particle disperser (manufactured by Microfluidics, model: M-110P) to prepare a coating solution for the charge transport layer, which was then allowed to stand at 20°C. An electrophotographic photoreceptor of Example 14 was prepared in the same manner as in Example 1, except for the above procedures.

[0156] [Example 15] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0157] In a soda-lime glass container, 8 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) were suspended in 36.4 g of tetrahydrofuran and stirred for 30 hours using a stirring blade. To the resulting silica filler suspension, 11.2 g of compound (1) represented by the above formula as a charge transport material, 15.6 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2040), and 111.8 g of tetrahydrofuran were added, mixed, and stirred for an additional 15 hours. The resulting mixture was degassed for 3 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A particle disperser (manufactured by Microfluidics, model: M-110P) was used for five-pass dispersion to prepare a charge transport layer coating solution, which was then allowed to stand at 20°C. An electrophotographic photosensitive member of Example 15 was prepared in the same manner as in Example 1 except for the above-mentioned operations.

[0158] [Example 16] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0159] In a soda-lime glass container, 3 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) were suspended in 13.7 g of tetrahydrofuran and stirred for 30 hours using a stirring blade. To the resulting silica filler suspension, 11.1 g of compound (1) represented by the above formula as a charge transport material, 23.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 127.4 g of tetrahydrofuran were added, mixed, and stirred for an additional 15 hours. The resulting mixture was degassed for 3 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A particle disperser (manufactured by Microfluidics, model: M-110P) was used for five-pass dispersion to prepare a coating solution for the charge transport layer, which was then allowed to stand at 20°C. An electrophotographic photosensitive member of Example 16 was prepared in the same manner as in Example 1 except for the above-mentioned procedures.

[0160] [Example 17] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0161] In a soda-lime glass container, 2 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) were suspended in 9.1 g of tetrahydrofuran and stirred for 16 hours using a stirring blade. To the resulting silica filler suspension, 12.6 g of compound (1) represented by the above formula as a charge transport material, 25.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 141.4 g of tetrahydrofuran were added, mixed, and stirred for an additional 15 hours. The resulting mixture was degassed for 3 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A particle disperser (manufactured by Microfluidics, model: M-110P) was used for five-pass dispersion to prepare a charge transport layer coating solution, which was then allowed to stand at 20°C. An electrophotographic photosensitive member of Example 17 was produced in the same manner as in Example 1 except for the above-mentioned operations.

[0162] [Example 18] The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0163] In a soda-lime glass container, 6 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment) were suspended in 27.3 g of tetrahydrofuran and stirred for 30 hours using a stirring blade. To the resulting silica filler suspension, 6.6 g of compound (1) represented by the above formula as a charge transport material, 10.5 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 77.8 g of tetrahydrofuran were added, mixed, and further stirred for 15 hours. The resulting mixture was degassed for 3 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A coating solution for the charge transport layer was prepared by five-pass dispersion using a particle dispersing device (manufactured by Microfluidics, model: M-110P) and allowed to stand at 20°C. An electrophotographic photoreceptor of Example 18 was prepared in the same manner as in Example 1, except for the above procedures.

[0164] [Comparative Example 1] An electrophotographic photoreceptor of Comparative Example 1 was produced in the same manner as in Example 1, except that in preparing the coating solution for the charge transport layer, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment) and 36 g of tetrahydrofuran were added to a polypropylene container, soda-lime glass beads with a diameter of 2 mm were added, and the mixture was stirred for an additional 15 hours in a ball mill. After that, the glass beads were removed, and then 18.0 g of compound (1) represented by the above formula as a charge transport material, 35.1 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., trade name: TS2040), and 179.0 g of tetrahydrofuran were added, mixed, and stirred for 30 hours.

[0165] Comparative Example 2 The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0166] In a soda-lime glass container, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) were suspended in 16 g of tetrahydrofuran and stirred for 10 hours using a stirring blade. To the resulting silica filler suspension, 5.1 g of compound (1) represented by the above formula as a charge transport material, 9.9 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 55.7 g of tetrahydrofuran were added, mixed, and further stirred for 15 hours. The resulting mixture was degassed for 5 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A coating solution for the charge transport layer was prepared by five-pass dispersion using a particle dispersing device (manufactured by Microfluidics, model: M-110P) and allowed to stand at 20°C. An electrophotographic photoreceptor of Comparative Example 2 was prepared in the same manner as in Example 1, except for the above procedures.

[0167] Comparative Example 3 The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0168] In a soda-lime glass container, 4 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment), 6.2 g of compound (1) represented by the above formula as a charge transport material, 12.0 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 83.6 g of tetrahydrofuran were added, mixed, and further stirred for 15 hours. The resulting mixture was degassed for 3 minutes using a Foamer Refiner ARE-310 (manufactured by Thinky Corporation). A five-pass dispersion process was performed using a particle disperser (manufactured by Microfluidics, model: M-110P) to prepare a coating solution for the charge transport layer, which was then allowed to stand at 20°C. An electrophotographic photoreceptor of Comparative Example 3 was prepared in the same manner as in Example 1, except for the above procedures.

[0169] Comparative Example 4 Silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL RX50, number average primary particle diameter 40 nm, bulk density 0.17 g / cm) were placed in a soda-lime glass container. 3 , true density 2.65g / cm 3 6 g of hexamethyldisilazane surface-treated charge transport material, 6.8 g of compound (1) represented by the above formula as a charge transport material, 13.3 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 87.3 g of tetrahydrofuran were added and mixed, followed by stirring for an additional 15 hours. The resulting mixture was degassed for 3 minutes using a Foamer Blender ARE-310 (manufactured by Thinky Corporation). A 5-pass dispersion treatment was performed using a particle dispersion device (manufactured by Microfluidics, model: M-110P) to prepare a coating solution for the charge transport layer, which was then allowed to stand at 20°C. An electrophotographic photoreceptor of Comparative Example 4 was produced in the same manner as in Example 1, except for the above procedures.

[0170] Comparative Example 5 The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0171] In a soda-lime glass container, 2 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) were suspended in 9.1 g of tetrahydrofuran and stirred for 30 hours using a stirring blade. To the resulting silica filler suspension, 12.6 g of compound (1) represented by the above formula as a charge transport material, 25.4 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 141.4 g of tetrahydrofuran were added, mixed, and further stirred for 15 hours. The resulting mixture was degassed for 3 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A coating solution for the charge transport layer was prepared by five-pass dispersion using a particle dispersing device (manufactured by Microfluidics, model: M-110P) and allowed to stand at 20°C. An electrophotographic photoreceptor of Comparative Example 5 was prepared in the same manner as in Example 1, except for the above procedures.

[0172] Comparative Example 6 The preparation process of the coating liquid for the charge transport layer was changed from that in Example 1 as follows.

[0173] In a soda-lime glass container, 6 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment) were suspended in 27.3 g of tetrahydrofuran and stirred for 20 hours using a stirring blade. To the resulting silica filler suspension, 6.6 g of compound (1) represented by the above formula as a charge transport material, 10.5 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), and 77.8 g of tetrahydrofuran were added, mixed, and further stirred for 15 hours. The resulting mixture was degassed for 3 minutes using a Foam-Removing Rentaro ARE-310 (manufactured by Thinky Corporation). A coating solution for the charge transport layer was prepared by five-pass dispersion using a particle dispersing device (manufactured by Microfluidics, model: M-110P) and allowed to stand at 20°C. An electrophotographic photoreceptor of Comparative Example 6 was prepared in the same manner as in Example 1, except for the above procedures.

[0174] [Measurement method, evaluation method and results] <Method for measuring the ten-point average roughness Rz of the surface layer and the average spacing Sm of irregularities on the surface layer> Rz and Sm were measured using a surface roughness measuring device (Mitutoyo Corporation, Surface Roughness Meter 1400D) under the conditions of a reference length of 0.8 mm, a cutoff wavelength of 0.8 mm, a measurement speed of 0.1 mm / sec, and a Gaussian cutoff type. The measurement position was the center of the axial direction of the electrophotographic photosensitive member.

[0175] <Method for measuring elastic power and Vickers hardness of photosensitive layer> The elastic power and Vickers hardness of the photosensitive layer were measured using a microhardness tester (Fisherscope H100V, manufactured by Fischer Instruments Co., Ltd.) by applying a maximum indentation load of 30 mN to the surface of the surface layer of the electrophotographic photoreceptor for 5 seconds under an environment of 25°C and 50% relative humidity. Vickers hardness was determined in accordance with JIS-Z-2244.

[0176] <Evaluation method> Each of the electrophotographic photoreceptors prepared in Examples 1 to 14 and Comparative Examples 1 to 8 was mounted in a unit of a digital copying machine (manufactured by Sharp Corporation, model: MX-B455W) modified for testing, and a developing unit was attached. The pressure at which the cleaning blade of the cleaning unit contacted the electrophotographic photoreceptor, i.e., the cleaning blade pressure, was adjusted to 21 gf / cm (2.05 × 10 -1 N / cm: initial linear pressure). A printing durability test was conducted by printing a character test chart (ISO19752) on 350,000 sheets of recording paper in an environment of 25°C temperature and 8% relative humidity.

[0177] (Method for evaluating printing durability) The thickness of the photosensitive layer at the start of the printing test and after 350,000 images were formed was measured using a film thickness measuring device (Filmetrics, Model: F-20-EXR). The difference between the film thickness at the start of the printing test and the film thickness after 350,000 images was used to determine the film thickness loss per 100,000 rotations of the photosensitive drum, and the printing durability was evaluated based on the obtained film thickness loss using the following criteria. The greater the film thickness loss, the worse the printing durability was evaluated.

[0178] -Judgment criteria- VG: Film loss per 100,000 revolutions is less than 0.50 μm It can also be used without problems in multifunction devices and printers that require a long life. G: The amount of film loss per 100,000 revolutions is 0.50 μm or more and less than 0.70 μm Although the amount of film loss is somewhat large, it can be used without any problems in devices other than multifunction devices and printers that require a long life. NB: The amount of film loss per 100,000 revolutions is 0.70 μm or more and less than 0.85 μm Although the amount of film loss is large, it can be used without any problems in inexpensive multifunction devices and printers. B: The amount of film loss per 100,000 revolutions is 0.85 μm or more The amount of film loss is large, which is problematic in terms of practical use.

[0179] (Method for evaluating crack resistance) In order to check the crack defect occurrence level of the electrophotographic photoreceptor, the output image during the printing durability test was checked to check whether cracks occurred on the image. Based on the presence or absence of cracks, the crack resistance was evaluated according to the following criteria.

[0180] -Judgment criteria- VG: No cracks. G: No cracks are observed on the image, but cracks are observed on the surface of the electrophotographic photosensitive member after the printing durability test. B: Image defects caused by cracks can be confirmed before 350,000 sheets are printed.

[0181] (Method for evaluating cleaning ability) In order to confirm the level of occurrence of cleaning defects of the electrophotographic photosensitive member after the printing durability test, the electrophotographic photosensitive member after 350,000 images were formed was attached to a unit of a digital copying machine (manufactured by Sharp Corporation, model: MX-B455W) modified for the test, and one untransferred image of 100% density was output on an A4 sheet of paper. Immediately after that, the copying machine was forcibly stopped, and the surface of the electrophotographic photosensitive member was visually observed, and the cleaning ability was evaluated according to the following criteria.

[0182] -Judgment criteria- VG: No cleaning defects occurred. G: One or two cleaning defects observed. It can be used without any problems with devices other than multifunction devices and printers that require high image quality. NB: 3 to 5 cleaning defects observed. It can be used without any problems with inexpensive multifunction devices and printers. B: Many (6 or more) cleaning defects were observed, which poses a problem in terms of practical use.

[0183] (Comprehensive evaluation method) Based on the evaluation results of the above evaluation items (printing durability, crack resistance, and cleaning properties), a comprehensive evaluation was made according to the following criteria.

[0184] -Judgment criteria- VG: VG rating in all categories, very good. G: Although some items may be rated G, all items are rated G or higher, and the product can be used without problems except for multifunction devices and printers that require a long life and high image quality. NB: Although some items are rated NB, all items are rated NB or better, and the product can be used without problems with inexpensive multifunction devices and printers. B: Any item has a B rating and cannot be used.

[0185] <Measurement and evaluation results> The results of measurement and evaluation of the electrophotographic photoreceptors prepared in Examples 1 to 14 and Comparative Examples 1 to 8 are listed in Table 1 below. In the table, "silica content" indicates the content of silica particles relative to the total solid content in the surface layer, "solid content of coating liquid" indicates the total ratio of the binder resin, charge transport material, additives, etc. in the coating liquid, "presence or absence of OCL" indicates the presence or absence of a surface protective layer, and "CL property" indicates cleaning property.

[0186] [Table 1]

[0187] As is clear from Table 1, the electrophotographic photoreceptors of Examples 1 to 18, which comprise a conductive support and a photosensitive layer formed on the conductive support, the photosensitive layer being composed of one or more layers, the surface layer of the photosensitive layer containing a binder resin, silica particles, and a charge transport material, the ten-point mean roughness Rz of the surface of the surface layer being 0.08 μm or more and 0.80 μm or less, the mean spacing Sm of the irregularities on the surface of the surface layer being more than 15 μm and 120 μm or less, and the ratio Sm / Rz of the mean spacing Sm to the ten-point mean roughness Rz being 30 or more and 500 or less, were excellent in terms of printing durability, crack resistance, and cleanability. In contrast, Comparative Examples 1 to 4, which did not satisfy these requirements, were inferior to the Examples in terms of printing durability and crack resistance. This is presumably due to insufficient dispersion of silica particles in the electrophotographic photoreceptor and inability to control surface properties, which resulted in increased damage to the photosensitive layer due to sliding printing of peripheral members.

[0188] Comparing Examples 1 and 2 with Example 3, it can be seen that Examples 1 and 2, in which the number-average primary particle diameter of the silica particles contained in the surface layer of the photosensitive layer is 10 nm or more, have better printing durability than Example 3, in which the number-average primary particle diameter of the silica particles is less than 10 nm. This is presumably because the silica particles are too small when the number-average primary particle diameter is less than 10 nm, resulting in insufficient anchoring effect. Comparing Examples 1 and 2 with Example 4, when the number-average primary particle diameter of the silica particles exceeds 30 nm, Sm and Sm / Rz tend to be large, increasing the external stress from the cleaning blade to the electrophotographic photosensitive member surface, which may lead to stress cracks in the electrophotographic photosensitive member or damage to the cleaning blade, making it difficult to achieve both high printing durability and good printing durability. Furthermore, when Sm and Sm / Rz are too small, it is believed that the contact area between the cleaning blade and the electrophotographic photosensitive member surface increases, increasing the external stress on the electrophotographic photosensitive member surface and increasing the risk of stress cracks, damage to the cleaning blade, etc. It is believed that by controlling Sm and Sm / Rz to appropriate values ​​as typified by Examples 1 and 2, the external load on the entire electrophotographic photosensitive member can be optimized.

[0189] Comparing Examples 1 and 2 with Example 5, it is clear that Examples 1 and 2, which have an Rz of 0.1 μm or more, have particularly superior cleaning properties compared to Example 5, which has an Rz of less than 0.1 μm. Although Example 5 improves printing durability by incorporating silica particles into the surface layer of the photosensitive layer, its Rz is too small, resulting in high friction with the cleaning blade, leading to chipping of the cleaning blade and causing poor cleaning. Comparing Examples 1 and 2 with Example 6, it is clear that Examples 1 and 2, which have an Rz of 0.5 μm or less, have particularly superior crack resistance compared to Example 6, which has an Rz of more than 0.5 μm. If the Rz exceeds 0.5 μm, the electrophotographic photosensitive member is susceptible to localized stress, which may lead to stress cracks. By controlling the Rz within the range of 0.1 μm or more and 0.5 μm or less, damage to the electrophotographic photosensitive member and cleaning blade can be reduced.

[0190] Comparing Examples 1 and 2 with Examples 7 and 8, it is found that Examples 1 and 2, in which Sm is 25 μm or more and 50 μm or less, have better crack resistance and cleaning properties than Example 7, in which Sm is less than 25 μm, and Example 8, in which Sm is more than 50 μm. Comparing Examples 1 and 2 with Examples 9 and 10, it is found that Examples 1 and 2, in which Sm / Rz is 100 or more and 200 or less, have better crack resistance and cleaning properties than Example 9, in which Sm / Rz is less than 100, and Example 10, in which Sm / Rz is more than 200. It is believed that by controlling the surface properties of the electrophotographic photosensitive member within the ranges of Sm of 25 μm or more and 50 μm or less and Sm / Rz of 100 or more and 200 or less, it is possible to suppress the stress that the cleaning blade and the electrophotographic photosensitive member impart to each other, thereby achieving a good balance of properties.

[0191] Comparing Example 7 and Example 11, it can be seen that similar effects can be obtained by controlling the dispersion state of the silica particles in the surface protective layer, which is the surface layer, even when a surface protective layer is provided and the photosensitive layer has a structure including a charge generation layer, a charge transport layer, and a surface protective layer, as in Example 11. However, because such a photosensitive layer structure increases the burden on production, it is more cost-effective to have the photosensitive layer comprised of a charge generation layer and a charge transport layer.

[0192] A comparison of Examples 1 and 12 with Example 13 reveals that Examples 1 and 12, in which the photosensitive layer has a thickness of 25 μm or more, have superior printing durability, crack resistance, and cleaning properties compared to Example 13, in which the photosensitive layer has a thickness of less than 25 μm. The photosensitive layer becomes thinner due to repeated fatigue, but as the layer becomes thinner, it tends to be more susceptible to electrical fatigue, which accelerates chemical degradation of the electrophotographic photoreceptor surface and tends to lead to adverse effects such as reduced printing durability and poor cleaning. Considering this tendency, a photosensitive layer thickness of 30 μm or more is more preferable in order to provide stable images over a longer period of time.

[0193] A comparison of Examples 1 and 2 with Example 14 shows that Examples 1 and 2, in which the photosensitive layer has a Vickers hardness (HV) of 26 or more, are superior in various evaluations to Example 14, in which the photosensitive layer has a Vickers hardness of less than 26. When the Vickers hardness value of the photosensitive layer decreases, the mechanical strength against repeated electrical fatigue tends to decrease, but by increasing the Vickers hardness to more than 26, it becomes possible to improve crack resistance and suppress cleaning defects.

[0194] A comparison of Example 1 with Examples 15 and 16 reveals that Example 1, in which the elastic power of the photosensitive layer is 41% or more and 48% or less, is superior in various evaluations to Example 15, in which the elastic power is less than 41%, and Example 16, in which the elastic power exceeds 48%. It can be seen that when the elastic power is reduced by selecting the constituent materials of the photosensitive layer, Sm / Rz decreases, and while printing durability is good, crack resistance and cleaning ability deteriorate, making it impossible to achieve a balance between these properties. On the other hand, when the elastic power is increased by selecting the constituent materials of the photosensitive layer, Sm / Rz tends to increase, and printing durability decreases.

[0195] A comparison of Example 1 with Examples 17 and 18 reveals that Example 1, in which the silica particle content in the surface layer of the photosensitive layer is 8% by mass or more and 25% by mass or less relative to the total solids content of the surface layer, is superior in various evaluations to Example 17, in which the silica particle content is less than 8% by mass, and Example 18, in which the silica particle content is more than 25% by mass. It is clear that increasing the silica particle content in the surface layer of the photosensitive layer tends to decrease Sm / Rz, and while printing durability is good, crack resistance and cleanability deteriorate, resulting in an imbalance between these properties. On the other hand, it is clear that decreasing the silica particle content in the surface layer of the photosensitive layer decreases printing durability and tends to increase Sm / Rz, increasing the risk of cracking.

[0196] [Other embodiments] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments, but should be defined by the claims. The technical scope of the present invention also includes all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0197] 1. Electrophotographic photoreceptor 11 Conductive support 14 Photosensitive layer 15 Charge generation layer 16 Charge transport layer (surface layer) 18 Undercoat layer 19 Silica particles (inorganic compound particles) 31 Exposure means (semiconductor laser) 32 Charging means (charger) 33 Developing means (developer) 33a Developing roller 33b casing 34 Transfer means (transfer charger) 35 Fixing means (fixing device) 35a Heating roller 35b Pressure roller 36 Cleaning means (cleaner) 36a cleaning blade 36b Recovery casing 37 Separation means 38 Casing 51 Recording media (recording paper or transfer paper) 100 Image forming device (laser printer)

Claims

1. A conductive support and a photosensitive layer formed on the conductive support, the photosensitive layer is composed of two layers, a charge generating layer and a charge transport layer, the charge transport layer corresponds to a surface layer of the photosensitive layer, the surface layer contains a binder resin, silica particles, and a charge transport material; The thickness of the surface layer is 10 μm or more and 40 μm or less, The number average primary particle diameter of the silica particles is 10 nm or more and 20 nm or less, the content of the silica particles in the surface layer is 8% by mass or more and 25% by mass or less with respect to the total solid content of the surface layer, the ten-point average roughness Rz of the surface of the surface layer is 0.08 μm or more and 0.80 μm or less; the average spacing Sm of the irregularities on the surface of the surface layer is more than 15 μm and 120 μm or less; An electrophotographic photoreceptor, wherein a ratio Sm / Rz of the average spacing Sm to the ten-point height of roughness Rz is 30 or more and 500 or less.

2. 2. The electrophotographic photoreceptor according to claim 1, An electrophotographic photoreceptor, characterized in that the elastic power of the photosensitive layer is 44.9% or more and 48% or less, as measured by applying a maximum indentation load of 30 mN to the surface of the surface layer for 5 seconds in an environment of a temperature of 25°C and a relative humidity of 50%.

3. 3. The electrophotographic photoreceptor according to claim 1, The electrophotographic photoreceptor is characterized in that the photosensitive layer has a thickness of 25 μm or more.

4. 4. The electrophotographic photoreceptor according to claim 1, The electrophotographic photoreceptor has a ten-point average roughness Rz of 0.1 μm or more and 0.5 μm or less.

5. 5. The electrophotographic photoreceptor according to claim 1, An electrophotographic photoreceptor characterized in that the average spacing Sm is 20 μm or more and 50 μm or less.

6. 6. The electrophotographic photoreceptor according to claim 1, an electrophotographic photoreceptor, wherein a ratio Sm / Rz of the average spacing Sm to the ten-point height of roughness Rz is 100 or more and 200 or less;

7. 7. The electrophotographic photoreceptor according to claim 1, An electrophotographic photoreceptor, wherein the Vickers hardness of the photosensitive layer is 26.5 HV or more and 28 HV or less, as measured in accordance with JIS-Z-2244 by applying a maximum indentation load of 30 mN to the surface of the surface layer for 5 seconds in an environment of a temperature of 25°C and a relative humidity of 50%.

8. The electrophotographic photoreceptor according to any one of claims 1 to 7, a charging means for charging the electrophotographic photosensitive member; an exposure unit that exposes the charged electrophotographic photosensitive member to light to form an electrostatic latent image; a developing means for developing the electrostatic latent image formed by exposure to form a toner image; a transfer means for transferring the toner image formed by development onto a recording medium; a fixing unit for fixing the transferred toner image onto the recording medium to form an image; a cleaning means for removing and recovering toner remaining on the electrophotographic photosensitive member; a charge eliminating means for eliminating surface charges remaining on the electrophotographic photosensitive member; An image forming apparatus comprising:

Images